Handover refers to a procedure which forwards a call signal from one base station to another base station as a user moves beyond a range or network software resets call path. A handover includes seamless and non-seamless handover. A seamless handover includes continuously maintaining a call.
According to an existing handover scheme between the LTE network and the non-3GPP, a user equipment (UE) performs connection with a target network without preliminary preparation for handover. Many carriers are deploying an evolved Packet Data Gateway (ePDG) to support IP Multimedia Subsystem (IMS) services (voice, video, rich communication services, and the like) and operator specific services. The services are comparable to what is deployed already in LTE network. The main function of the ePDG is to secure the data transmission with a UE connected to the evolved packet core (EPC) over an untrusted non-3GPP access. For this purpose, the ePDG acts as a termination node of IPsec tunnels established with the UE.